1. Field of the Invention
This invention generally relates to communication systems. In particular, an exemplary embodiment of this invention relates to estimating communication channel capacity. More particularly, an exemplary aspect of the present invention relates to estimating digital communications channel capacity.
2. Description of Related Art
Digital Subscriber Line (DSL) technology makes it possible to transport high bit rate digital information via a communications channel, such as a subscriber line. The channel capacity, which is defined as the obtainable data rate for a given line, is based on the physical structure and topology of the line, such as the length of the line, gauge, existence of bridged taps, bridged tap locations and lengths, etc. Thus, if the topology of the line is known, the data rate can be predicted prior to providing DSL service to a customer.
Time domain reflectometry (TDR) is a very useful tool for characterizing a subscriber line. TDR operates by sending an electrical pulse down the line and measuring the returned signal, referred to as a TDR echo. The measured TDR echo contains information about the physical structure and topology of the line.
The most common method for evaluating the channel capacity from a TDR echo is by explicitly estimating the physical topology of the line based on the transmission line theory, and then searching a database to find a data rate corresponding to the specific topology. One issue with this approach is the estimation complexity increases dramatically when the topology of the line is complex. For example, consider a line with N consecutive sections of different gauges but without bridged taps. Since there are two variables that need to be estimated for each section, the gauge and the length, the searching space is 2N dimensional. Thus, the computation complexity increases exponentially with the number of distinct sections.